Imprinting Diversity

By Cristina Luiggi
Imprinting Diversity
Joachim Messing talks about how genomic imprinting may be a strong driver of diversity.
Sexual reproduction yields offspring with two copies of the same gene, one from each parent; but in an epigenetic phenomenon known as genomic imprinting, only one copy of certain genes is turned on or off, depending on which parent contributed it. Imprinted genes are stamped by patterns of DNA methylation or histone modification during g

By Cristina Luiggi | March 1, 2011

Imprinting Diversity

Joachim Messing talks about how genomic imprinting may be a strong driver of diversity.

Sexual reproduction yields offspring with two copies of the same gene, one from each parent; but in an epigenetic phenomenon known as genomic imprinting, only one copy of certain genes is turned on or off, depending on which parent contributed it. Imprinted genes are stamped by patterns of DNA methylation or histone modification during gamete formation, and their activation or inactivation is then passed on to offspring. Previously, approximately 100 genes were thought to be imprinted in mammals. But Rutgers University molecular biologist and F1000 Member Joachim Messing, discusses a recent paper that found many more imprinted genes in mammals, suggesting this may be a major form of epigenetic regulation (Science, 329:643-48, 2010).

Audio: Messing on imprinting and diversity

Download Flash player to listen to Joachim Messing discuss how genomic imprinting may drive diversity

Joachim Messing on how genomic imprinting may drive diversity

The Scientist: What’s an evolutionary justification for the parental bias in gene expression encoded by genomic imprinting?

Joachim Messing: The genes that were initially discovered to be imprinted in mammals were those that had an influence on the development of the embryo. So that led to the hypothesis that there are competing interests between the two parents in the offspring, and that only genes having to do with a conflict of interests between the two parents are imprinted. The female has to balance the allocation of resources between herself and her offspring, while the male wants the resources to go primarily to the offspring. From a selection point of view, the male sperm will promote the growth of the offspring, whereas the female has to be able to reproduce more often, so she has to be careful in allocating the resources.

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TS: Catherine Dulac of Harvard University and colleagues identified a whopping 1,300 imprinted genes representing a wide range of functions in the mouse brain. How does this discovery change our understanding of genomic imprinting?

JM: That was something that I think most of us didn’t expect. They discovered that there are not just a handful of genes that might play a role in growth—there are more than a thousand genes that are implicated in parental imprinting. So it may have nothing to do with this conflict theory. The wide array of genes that develop this way may only argue for the evolution of sexual reproduction as something essential. Imprinting selects for sexual reproduction by requiring an offspring to inherit genetic information from two individuals in order to have a functional gene set. The consequence of that is that you also get genetic exchange through the recombination of homologous chromosomes, so that all the variation in gene function that is manifested over the years in a population is exchanged and creates new variants. In mammals this is the only way of creating diversity.

Maybe the need for sexual reproduction is to increase diversity. So maybe there was a greater selective pressure to ensure that offspring will only survive if they are the result of sexual reproduction.

TS: Previous research in mammals identified the brain, particularly the hypothalamus, as a hotspot for imprinted genes. The current study found that imprinted genes differ in which parental influence predominates across the brain, and that maternally imprinted genes predominate in the fetal brain, whereas paternally imprinted genes play a larger role in the adult brain. Why is this so?

JM: The greatest diversity that we need in terms of gene expression is probably in the brain because the brain has the most complex function of all organs. Because each offspring can have such a unique combination of abilities, there must be a mechanism by which you can create this diversity during development. What I find very interesting is the hypothesis that diversity is created through another well-known mechanism known as transposition, in which mobile DNA sequences are integrated into other genes, potentially creating mutations. So you get a fine-tuning of what you want to achieve in terms of the interplay of different proteins in the brain. I found it very intriguing that there is this differential activation or mobilization of transposable elements in the brain, which itself is also epigenetically regulated. What applies to transposable elements certainly would fit here with the finding that imprinted genes are affecting function in the brain.

TS: How do defects in genomic imprinting contribute to human diseases, such as Prader-Willi and Angelman syndromes?

JM: A diploid genome has the advantage of usually having a backup for every gene copy. But that’s not true for imprinted genes. If you have a mutation in the copy that is working, there is no compensation from the silenced copy on the other chromosome, and that makes you very vulnerable.

F1000 Member Joachim Messing’s lab studies plant genes that regulate nitrogen and amino acid storage in the seed. You can access his F1000 evaluation of the paper here.

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Enough Is Enough!\nIt Is Not "Genomic Imprinting Affects Diversity"\nIt Is "Culture/Diversity Imprints Genetics".\n\n\nPart I\n======\n\nA. "Imprinting Diversity"\nhttp://www.the-scientist.com/2011/3/1/26/1/#messing\n\n\nB. On Human-Primate Diversity\n\n"Aging rates, gender gap in mortality similar across all primates"\nhttp://www.eurekalert.org/pub_releases/2011-03/du-arg030711.php\n\n"Age affects us all"\nhttp://www.eurekalert.org/pub_releases/2011-03/uonc-aau030611.php\n\n\nC. Again And Again: It's Culture That Modifies Genetics\n\nBut in the case of human-primates the process takes millions of years because the original primate physiological genetics are better conserved in huimans than in their original primate relatives. In humans the modifications are in the brains, in evolving capabilities to modify their environments and toolings, whereas their relative primates need to continuously adapt\nphysiologically to changing environments. Humans modify environs, their forefathers adapt to environs.\n\n\nD. On Uniquely Human Traits\n\nHorse And Wagon, Culture And Genetics\n\nIt's Culture That Modifies Genetics, Not Genetics That Modifies Culture!\n\n"How DNA deletions may have produced uniquely human traits"\nhttp://www.the-scientist.com/news/display/58044/\n\nWith such a title you don't need to read the article; it would apparently explain how a wagon pulls the horse.\n\nSee \n"Seed of Human-Chimp Genomes Diversity"\nhttp://pulse.yahoo.com/_2SF3CJJM5OU6T27OC4MFQSDYEU/blog/articles/53079\n\n\nDov Henis\n(Comments from 22nd century)\nhttp://www.the-scientist.com/community/user/profile/1655.page\n\n\nPart II\n=======\n\nFrom a letter I recently e'mailed elsewhere re "Big Brains And Spineless Penises"\nOr "Sex, Spines And Human Evolution":\n\nNow, from where comes such scientific ignorance to Stanford?\nLike most science ignorance (and there's plenty of it around) it flows mainly from the following "spring of creativity":\n\n\nA. Genes/genomes are ORGANISMS, subject to natural selection.\n\nUpdate comprehension of cosmos and life evolution.\n\nApply Critical Thinking For Solving THE RIGHT USA SCIENCE PROBLEM\n\nWhy Life Eats And Why Life Sleeps:\nLife eats because the universe expands.\nLife sleeps because when RNAs genesised there was not yet biometabolism. \n\nUS losing lead in science? \n\n"The proportion of papers authored by US researchers, Wagner reported, dropped by 20 percent from 1996 to 2008."\nNews From AAAS\nhttp://www.the-scientist.com/news/display/57994/\n\nJust the proportion of the "papers"? \nOtherwise the US "papers" have been, are, and prospected to be of scientific value? \n\nSee "Hope For Science?"\nhttp://pulse.yahoo.com/_2SF3CJJM5OU6T27OC4MFQSDYEU/blog/articles/248628\n\nAnd see the following two E-medium samples, thus presently taboo, nonAAASkoshered nonpeerreviewable notes:\n\n===========================\n\n1st sample\n\nGenes And Genomes Are Both Organisms\n\nGenomes Are RNA-Evolved Template ORGANISMS \nEpiDNAtics Is Not Epigenetics\n\nFrom "Dispel Some Figments Of 2010 Science Imagination"\nhttp://pulse.yahoo.com/_2SF3CJJM5OU6T27OC4MFQSDYEU/blog/articles/245540\n\nThe "heritable or enduring changes" are epiDNAtics, not epigenetics. Alternative splicing is not epigenetics, even if/when not involving alteration of the DNA sequence. Earth life is an RNA world.\n\nIt's the RNAs that evolve proteins. AND IT'S THE RNAs THAT HAVE EVOLVED AND PRODUCE AND EMPLOY THE RNA and (stabler) DNA template genome organisms for carrying out life processes, i.e. for enhancing Earth's biosphere by proliferating RNAs, for augmenting and constraining as long as possible some energy by augmenting its, RNA's, self-propagation, constraining temporarily some of the total energy of the universe, all of which is nevertheless destined to fuel the ongoing cosmic expansion. \n\nIT HAS ALWAYS BEEN AND IT STILL IS AN RNA EARTH LIFE.\n\nScience should adjust its vision, comprehension and concepts. \n\n\nDov Henis \n(comments from 22nd century)\n\n==========================\n\n2nd sample\n\nSuggested 2010 Updated Concepts Of Evolution, Natural Selection\nhttp://pulse.yahoo.com/_2SF3CJJM5OU6T27OC4MFQSDYEU/blog/articles/261519?listPage=index\nhttp://pulse.yahoo.com/_2SF3CJJM5OU6T27OC4MFQSDYEU/blog/articles/261527?listPage=index\n\nOn The Nature And Origin Of Cosmic, Including Life, Evolution, Beyond Darwin And Einstein\n\nThe purpose of OUR life and of its promotion is ours to formulate and set. It derives solely from our cognition. The nature and origin of cosmic, including life, evolution:\n\nNatural Selection Derives From Cosmic Expansion\n\n"Evolution is energy temporarily constrained in a mass format to postpone reconversion of the mass to the energy fueling the cosmic expansion".\n\nI.\n\nOrigin And Nature Of Natural Selection\n\nLife is another mass format, a self-replicating mass format.\nAll mass formats are subject to natural selection.\nNatural selection is the delaying conversion of mass to the energy fueling cosmic expansion.\nCosmic expansion is the reconversion of all mass to energy.\n\nNatural Selection Updated 2010, Beyond Historical Concepts:\n\nNatural Selection applies to ALL mass formats. Life, self-replicating format, is just one of them.\nNatural Selection Defined:\n\n Natural selection is E (energy) temporarily constrained in an m (mass) format. Period. \n\nNatural selection is a ubiquitous property of each and every and all cosmic mass, spin array, formats. Mass strives to increase its constrained energy content in attempt to postpone its reconversion to energy and to postpone addition of its constitutional energy to the totality of the cosmic energy that fuels the cosmic expansion going on since Big Bang. \n\n\nDov Henis\n(Comments From The 22nd Century)\n\nCosmic Evolution Simplified\nhttp://www.the-scientist.com/community/posts/list/240/122.page#4427\nGravity Is The Monotheism Of The Cosmos\nhttp://www.the-scientist.com/community/posts/list/260/122.page#4887\n\n\nII.\n\nLongevity Schmongevity Genes?\n\nIt's Not The Procedure, But The Concept That Is Absurd \n\nLongevity Genes Search Reflects Science Decadence \nhttp://www.the-scientist.com/community/posts/list/320/122.page#6368\n\nA. "For most centenarians, longevity is written in the DNA."\n\nA study of people who live past 100 reveals many genetic paths to a long life.\nhttp://www.sciencenews.org/view/generic/id/60772/title/For_most_centenarians%2C_longevity_is_written_in_the_DNA\n\n\nB. Longevity is about survival, which is about "natural selection", which is about energy constrainment, which is about life evolution, which is about cosmic evolution. All mass is destined to reconvert to energy to fuel the ongoing cosmic expansion. This is why organisms and black holes etc., eat, digest energy in mass forms, to delay-postpone conversion to energy. This is evolution, which is natural selection, which is survival, which is longevity.\n\nAll mass formats age, degenerate back into enery. Life is a mass format. Searching for longevity genes is searching for evolution genes...\n\n\nC. The search for longevity genes is a reflection of the 20th-21st centuries science decadence\n\nIts concepts and terminology reflect the abandonment of basic science for adoption of the pretentious cancerous capitalist 20th-21st century technology culture.\n\n\nDov Henis\n(Comments From The 22nd Century)\n\n\nIII.\n\nRethink Astronomy And The Universe\n( even without Quantum Unique Ergodicity, but with plain commonsense )\n\nGalactic clusters formed by dispersion, not by conglomeration. The proof of this is their behaviour, including acceleration, as Newtonian bodies. \n\nThese bodies formed at the start of inflation, when all energy was still in mass format, and the inflation was the start of reconversion of cosmic mass into energy. Cosmic expansion acceleration rate differs for galactic clusters, proceeding according to Newton's laws, proportional to the various galactic clusters' masses.\n\n\nRethink\n- A Basic Physics Tenet\n- The Universe In Which We Live\n\nA. "Neutrino quick-change artist caught in the act"\n\nA transformation from one ?flavor? to another confirms the elusive elementary particles have mass and suggests a need for new physics.\nhttp://www.sciencenews.org/view/generic/id/59825/title/Neutrino_quick-change_artist_caught_in_the_act\n\n\nB. Adopt \n\n- Each and every particle has mass. \n- Dark energy and dark matter YOK. All the universe energy and mass are plainly accounted for.\n- Higgs field/particle YOK. Mass forms below some value of D in E=Total[m(1 + D)] .\n- Do not be afraid of embarrassingly obvious answers. Adopt space-distance in lieu of space-time. \n\n\nC. And Rethink The Universe:\n\nBy the presently available data our universe is a dual-cycle array, between the mass and energy poles.\n\nOne cycle, the present, started from singularity, with all cosmic energy in mass format, and it has been proceeding to reconvert all the mass resolved at the Big Bang back to energy, by expanding the cosmos, by accelerating away the galaxy clusters. \n\nThe other cycle, the cycle leading to singularity, will re-start when expansion consumes most of the mass that fuels it. Gravity will then overcome expansion and initiate reconversion of all the energy back to mass, to singularity, again. \n\n\nDov Henis\n(Comments From The 22nd Century)\n\nDispel Some Figments Of 2010 Science Imagination\nhttp://pulse.yahoo.com/_2SF3CJJM5OU6T27OC4MFQSDYEU/blog/articles/245540\n03.2010 Updated Life Manifest \nhttp://www.the-scientist.com/community/posts/list/54.page#5065\n28Dec09 Updated "Implications Of E=Total[m(1 + D)] "\nhttp://www.the-scientist.com/community/posts/list/180/122.page#3108\nEvolution, Natural Selection, Derive From Cosmic Expansion\nhttp://darwiniana.com/2010/09/05/the-question-reductionists-fear/

The arguments here presented as alternatives to conflict theory don't hold up. Sex has to come before imprinting, otherwise imprinting is unfit. If a mutation arose when sex was not obligatory, causing imprinting promoting the need for sex, it would be less fit in offspring produced without sex and so would render itself extinct. As far as I am aware, imprinting only exists in species where mothers provide investment in offspring AFTER the egg is fertilised, typically plants and mammals where fertilised eggs develop on nutrient provided by the mother, and genes in the embryo can influence that food provision. If imprinting went with sex it should be found in all sexual species, including egg layers such as Drosophila, but it isn't. The reason for paternal genes being active in brains after birth is probably that female mammals are obliged to suckle and guard their offspring, and gene activity in the offspring causing behaviour that intensifies maternal support (at the expense of other offspring) is selected in the paternal gene set. The conflict is with half-sibs as well as the mother. There could be a case for imprinting in species such as birds where care after hatching is provided by one parent.

Males and females are selected for different behaviours. The maternal X equally ends up in male or female offspring. Male Xs only end up in daughters so hypothetically should be imprinted to promote behaviour advantageous in females. Hence lots of imprinting of neurological genes on the X?